Polypropylene has been used in many applications in the form of molded articles, film, sheet, etc., because it is excellent in molding processability, toughness, moisture resistance, gasoline resistance, chemical resistance, has a low specific gravity, and is inexpensive. The use of polypropylene is expanding at an increasing rate in the fields of exterior and interior automotive trims, in electrical equipment device housing and covers as well as household and personal articles.
However, polypropylene is poor or inadequate in heat resistance, stiffness, scratch resistance and impact resistance. These deficiencies are obstacles to opening up new applications for polypropylene, particularly applications which have traditionally been injection molded. In order to overcome these shortcomings, especially inadequate impact resistance, polypropylene has been blended with a rubbery elastic material such as ethylene-propylene copolymer rubber, ethylene-propylene-diene copolymer rubber or ethylene-butene copolymer rubber. For example, U.S. Pat. No. 5,391,618 discloses low crystalline polypropylene polymer compositions containing an ethylene-alpha-olefin copolymer. Additionally, U.S. Pat. No. 5,576,374 describes polypropylene polymer compositions with a substantially linear ethylene polymer. Another example, U.S. Pat. No. 5,639,829, discloses propylene polymer compositions containing an ethylene and 1-butene random copolymer. Each of these patents is incorporated herein by reference.
To achieve a good balance of stiffness and toughness, U.S. Pat. No. 6,300,419, incorporated herein by reference, employs compositions containing a high crystalline polypropylene, a substantially linear ethylene polymer, a filler, an additional polymer, and a slip agent, such as an unsaturated fatty acid amide. Scratch resistance, while addressed in these earlier patents, has not yet been improved in a manner sufficient to satisfy the current demand in the automotive and other relevant industries. Accordingly, a need exists in the art for a polypropylene composition that overcomes such shortcomings while also providing superior scratch resistance. This invention answers that need.